Shared Thunderbird Folders Apparently Trashed by Thunderbird 3 Beta 4

[Bill]

I've been running Fedora since before it was Fedora. It's my main
file server and holds my Thunderbird mailboxes. These mailbox folders
are shared between various Thunderbird clients on Windows, Linux, and
Mac computers. No matter which computer I use, I can get to
Thunderbird and check my mail.

A couple of days ago I installed Fedora 12 on my mail file server.
When I fired up Thunderbird on my file server I was taken by surprise:
it used a completely new interface and began rearranging my mail. Now
I realize I have inadvertently installed a BETA!!! version of
Thunderbird (thanks, Fedora!) and I can't read my mail on any computer
in the house except the F12 box. I have found the instructions for
going back to the previous view (separate folders for my various
inboxes) and have done that. I can see mail on F12 but on the other
Thunderbirds using the same mail storage, although I see the folder
names, nothing but an hourglass appears when I try to click on a
folder name.

Help! How can I revert mymail folders to be usable by other
Thunderbird clients?